A variety of electronic components utilize voltage controlled oscillator (VCO) circuits. A VCO circuit provides a frequency output that is proportional to an applied voltage. Providing clock signals, producing accurate waveforms, and providing feedback signals are among the many possible uses of VCO circuits. VCO circuits are typically used, for example, in computers, computer peripherals, counters, timers, calculators, oscilloscopes, and wireless electronic equipment, including cellular telephones and other communication devices.
One example of a device that may use a VCO circuit is a Switching-Mode Power Supply (SMPS). An SMPS enables an electrical device to operate from a variety of different power supplies, and may be included in electronic components ranging from computers, automotive components, aircraft systems, cellular telephones and other types of communication devices and systems. Modern SMPS typically use resonant switching techniques to reduce switching losses and allow high-frequency operation, thus increasing power density. One important topology for such SMPS applications is known as the LLC resonant half bridge which senses an output voltage, generates a feedback signal, and then uses this feedback signal to control an operating switching frequency of the SMPS. Although desirable results have been achieved using conventional topologies, there is room for improvement.